This invention relates to additives useful in preparing polyurethane formulations to impart specific properties to the final polyurethane product.
As is well known in the polyurethane art, polyurethanes can be prepared in a variety of forms. One commonly prepared form includes foamed polyurethanes, in which the density of the product is reduced by introduction of a blowing agent. Foamed polyurethanes are frequently molded into a desired final shape, and may be categorized as flexible, i.e., relatively low density, foams or as semi-flexible, i.e., relatively higher density materials. Polyurethanes may also be prepared as elastomeric compositions. in which there is little or no density reduction and also often significant stiffness, as is the case with reaction injection molded (RIM) materials.
In the case of molded materials, a frequently encountered problem is that of release of the cured polyurethane article from the mold. Various approaches have been tried to solve this problem with varying success. Some notable examples include the use of a metal carboxylate salt, such as zinc stearate, as is disclosed in, for example, U.S. Pat. Nos. 4,876.019 and 4,585,803. This additive is particularly successful in increasing the number of releases of a RIM article from the mold without undesirable sacrifice of the final physical properties of the article.
Another problem encountered in preparing molded polyurethane materials is that, for a number of applications particularly including automotive interior applications, the molding of the polyurethane is done directly on a sheet, or "cladding," of a vinyl-based polymer such as polyvinyl chloride. Over time there is a well-known tendency for the vinyl-based polymeric cladding to discolor or "stain", thereby reducing the marketability of the final product. Exposure to climatic extremes, such as is encountered by polyvinyl chloride-clad polyurethanes in vehicle dashboards, increases the rate of this staining.
Finally, it is well known in the art that certain catalysts are needed for many formulations in order to ensure adequate polyurethane cure to allow relatively rapid demolding time. For many purposes, especially in the automotive industry, such demolding is preferably accomplished in less than about 60 seconds from injection of the reactants into the mold. To speed the reaction and thereby allow processing by automated RIM equipment, tin carboxylate catalysts are frequently used, such as, for example, dimethyltin dilaurate.
Thus, it would be desirable to find an additive or group of additives for use in polyurethane formulations that enhances mold release properties, particularly as to multiple releases; that reduces the staining or discoloration of vinyl-based polymeric cladding adhered thereto; and that shows sufficient catalytic activity to allow for acceptable demolding times for use particularly in automated processes of various kinds.